STRUCTURAL FLUCTUATIONS BETWEEN 2 CONFORMATIONAL STATES OF A TRANSMEMBRANE HELICAL PEPTIDE ARE RELATED TO ITS CHANNEL-FORMING PROPERTIES IN PLANAR LIPID-MEMBRANES

Putative transmembrane helices of membrane proteins in general and channel proteins in particular often contain proline residues which may induce a bend into an otherwise regular helical structure. Here we show by fluorescence-energy-transfer measurements and molecular-dynamics calculations that, in the case of synthetic bilayer-spanning helical polypeptides, a proline-induced bend in a helix acts as a flexible element mediating rigid body motions of the helical segments. Most important, such structural fluctuations in the transmembrane helices seem to play a functional role in the formation of ionic channels in planar lipid bilayers and biological membranes.